The aim is to enable the quality of welding to be monitored while welding is actually being carried out, and thus to enable the welding conditions to be immediately modified so as to improve the quality of welding if this is seen to be defective.
For achieving this aim I have already proposed an apparatus, more specifically a sensor (preferably an induction sensor) by means of which the relative displacement of welding electrodes can be measured as a function of time, that is to say either the penetration of the bars into one another or the expansion of the sheets at the welding point can be measured by this sensor. The curve thus obtained can be considered as the physical result of interaction of the various operating values (current strength, force at the electrodes, welding time) and, on this basis, as a genuine output value on which any regulation of the welding process can be based.
I have also proposed equipment which comprises, considered singly or in combination:
a sensor by means of which the electrical energy dissipated during the welding operation can be measured as a function of time,
a sensor by means of which the pressure applied to the two welding electrodes can be measured, as a function of time, by any suitable means
a sensor by means of which the speed of relative movement of the electrodes can be measured, as a function of time, that is to say by means of which it is possible to measure either the speed of penetration of steel bars into one another or the speed of expansion of sheet steels at the welding point.
The results obtained with this equipment have been found to be very satisfactory but, in certain cases, the installation of the movement sensor entails difficulties either due to the large amount of space occupied or by reason by disturbances in the measurement carried out.
Underlying the present invention is the object of providing an apparatus by means of which these drawbacks can be remedied.